Exhaust systems having water traps in a variety of embodiments, and the materials required therefor, are described in Published International Patent Document No. WO 96/39576. After an internal combustion engine has been started, the onset of pollutant conversion in a three-way catalytic converter in the exhaust of the internal combustion engine in motor vehicles is particularly important in terms of compliance with increasingly stringent exhaust gas limit values. The onset of pollutant conversion depends on the activation temperature of the catalytic material and on the speed with which that activation temperature is reached after a cold start. Published International Patent Document No. WO 99/34902 describes that the activation temperature of the three-way catalytic converter can be considerably lowered if the support of the catalytically active material can be kept substantially dry. Moisture in the form of small water droplets occurs preferentially in the exhaust gas after a cold start of the internal combustion engine. As soon as the engine and the exhaust system are sufficiently warm, no further droplet formation occurs. In order to keep the catalytic converter dry after a cold start, a water trap (water adsorber) can be positioned upstream from the catalytic converter. A water trap collects water and water vapor below a certain temperature. Attainment of the activation temperature of the three-way catalytic converter can be additionally accelerated by so-called chemical heating. This utilizes the fact that if no water vapor is present, the CO exhaust component oxidizes at room temperature to CO2 and releases a large quantity of heat. The catalytic converter 28 can be equipped with a coating that promotes the exothermic reaction of CO to CO2. At low temperatures (e.g. at room temperature) the exothermic reaction process is extremely sensitive to water vapor. In other words, in the presence of water vapor the reaction occurs in only attenuated fashion or not at all. With regard to this chemical heating process as well, it is advantageous to remove water vapor from the exhaust gas with a water adsorber and to store it temporarily in the water adsorber. As the temperature of the exhaust gas and the exhaust system rises, the water stored in the water adsorber is then desorbed, and the water adsorber once again becomes receptive. The desorbing water does not interfere with pollutant conversion when the exhaust system is hot. Pollutant conversion after a cold start thus depends substantially on the functionality of the water adsorber. Any disruption in functionality should therefore be detected and remedied as quickly as possible.